1. Field of the Invention
The present invention relates to the field of flat panel displaying, and in particular to a backlight module and a liquid crystal display device using the backlight module.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus of wide applications, such as mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and notebook computer screens.
Most of the liquid crystal displays that are currently available in the market are backlighting liquid crystal displays, which comprise an enclosure, a liquid crystal panel arranged in the enclosure, and a backlight module mounted in the enclosure. The structure of a conventional liquid crystal panel is composed of a color filter (CF) substrate, a thin-film transistor (TFT) array substrate, and a liquid crystal layer arranged between the two substrates and the principle of operation is that a driving voltage is applied to the two glass substrates to control rotation of the liquid crystal molecules of the liquid crystal layer in order to refract out light emitting from the backlight module to generate images. Since the liquid crystal panel itself does not emit light, light must be provided from the backlight module in order to normally display images. Thus, the backlight module is one of the key components of the liquid crystal displays. The backlight modules can be classified in two types, namely a side-edge backlight module and a direct backlight module, according to the site where light gets incident. The direct backlight module comprises a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), which is arranged at the backside of the liquid crystal panel to form a planar light source directly supplied to the liquid crystal display panel. The side-edge backlight module comprises an LED light bar, serving as a backlight source, which is arranged at an edge of a backplane to be located rearward of one side of the liquid crystal display panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face at one side of the light guide plate and is projected out of a light emergence face of the light guide plate, after being reflected and diffused, to pass through an optic film assembly so as to form a planar light source for the liquid crystal panel.
Referring to FIG. 1, which is a schematic view showing an essential structure of a conventional side-edge backlight module, which comprises: a backplane 100, a light guide plate 300 that is arranged in the backplane 100 and a backlight source 500 that is arranged in the backplane 100 and located at one side of the light guide plate 300, an optic film assembly 700 arranged on the light guide plate 300, and a mold frame 900 that is arranged on the backplane 100.
However, the backlight module 1 shown in FIG. 1 is readily susceptible to light leaking (which means light emitting from the backlight source 500 is transmitted out directly through the optic film assembly 700). To cope with such a problem, a backlight module (as shown in FIG. 2) having a barrier wall 902 formed n the mold frame 900′ is available to reflect back the leaking light.
With the development of the LCD industry, consumers' request for LED bezel is increasingly heightened. For the arrangement of side-edge lighting illustrated in FIG. 2, due to the limitation imposed by the barrier wall 902 of the mold frame 900′, it is generally difficult to achieve bezel slimming. For the purposes of achieving bezel slimming, the solution illustrated in FIG. 3 is commonly adopted, in which the optical film assembly 700″ are positioned on the mold frame 900″. Such an arrangement enables the achievement of narrowing of the bezel but also brings other issues. For example, the optic film assembly 700″ may readily get separated, making it difficult to fix.
Other arrangements is also known, such as positioning the optic film assembly 700″′ under the mold frame 900″′ (as shown in FIG. 4). To prevent light leaking, the lowermost one of the films of the optic film assembly 700″′ is extended in the light incidence side to a surface of a printed circuit board (PCB) of the backlight source 500′ and a circumference of the lowermost film or even all the films is blacked. This increases the operations of processing the optic film assembly 700″′ and a lower yield rate may result, leading to an increase of the cost.